The invention relates to a method for determining a path between a first and a second radio station of a radio communications system. In addition, the invention relates to a radio installation for carrying out said method.
In radio communications systems, information (for example, voice, picture information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data is transmitted by using electromagnetic waves over a radio interface between the sending and the receiving radio station. In this case, the radio stations involved can be, depending on the specific development of the radio communications system, various kinds of radio stations, radio access points or base stations on the subscriber side. Therefore, the electromagnetic waves in this case are radiated using carrier frequencies which lie in the frequency band provided for the specific system.
Radio communications systems are often embodied as cellular systems, for example, according to the GSM (Global System for Mobile Communication) standard or the UMTS (Universal Mobile Telecommunications System) standard with a network infrastructure having, for example, base stations, installations for checking and controlling the base stations and additional installations on the network side. For the cellular GSM mobile radio system, frequencies at 900, 1800 and 1900 MHz are used.
In addition to these wide-area organized (supralocal) cellular, hierarchical radio networks, in this case wireless local networks (WLANs, Wireless Local Area Networks) with a usually spatially more clearly defined radio coverage area are also available. The cells covered by the WLAN access points (AP: Access Point) with a diameter of up to a few hundred meters are small compared to usual mobile radio cells. Examples of different standards for the WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM. However, in particular in the USA and in Europe, almost exclusively products based on the IEEE 802.11 family seem to be gaining recognition at present as the local radio-supported networks.
In many WLANs, radio stations can communicate directly with each other on the subscriber side over one or more hops (hop or multihop). In addition, they can send and receive data via the WLAN access points (AP: Access Point), which are usually connected to other communications networks. The connection of a radio station on the subscriber side to a radio access point can take place either directly or over hops by routing the data through other radio stations.
In general, WLANs use the unlicensed frequency range around 2.4 GHz, in which the data transmission rates are up to 11 Mbit/s. It is possible to operate future WLANs in the 5 GHz range and reach data rates exceeding 50 Mbit/s. In this way, data rates are made available to the subscribers of the WLANs, said data rates being considerably higher than those which will be offered by the third mobile radio generation (for example, UMTS).
Access by radio stations to joint radio resources of the transmission medium, such as for example time, frequency, power or space, is controlled in the case of radio communications systems by multiple access methods (Multiple Access, MA). In the case of orthogonal frequency multiple access methods commonly known as orthogonal frequency division multiplex methods (OFDM, Orthogonal Frequency Division Multiplex), a broad frequency band is subdivided into a plurality of a plurality of narrowband subbands. One subband, more subbands or all the subbands are assigned to the radio stations for purposes of communication.
In an adhoc mode of a radio communications system, radio stations on the subscriber side transmit data to each other without it being necessary to route this data through a central installation. In this case, the connection between two radio stations on the subscriber side takes place either directly or, in the case of greater distances, via additional radio stations on the subscriber side which form relay stations for this connection. The radio stations on the subscriber side of such a self-organized network can be mobile radio stations (for example, mobile radio equipment of persons or in passenger cars) on the subscriber side and/or predominantly stationary radio stations (for example, computers, printers, household appliances) on the subscriber side.
Before data can be transmitted between two radio stations on the subscriber side in an adhoc mode of a radio communications system, a path must first be determined between these two radio stations. Said path extends over a plurality of a plurality of radio stations which route the data. Also in the case of a radio station of a WLAN on the subscriber side, which is located outside the direct radio coverage area of the radio access point, a path must be determined between the radio station and the radio access points on the subscriber side before a communication between the radio station on the subscriber side and the radio access point can take place. The determination of a path through a radio communications system is called routing.